Environmental concerns are driving increased emphasis on reductions in gas turbine exhaust emissions, both from a regulatory and financial perspective, such as landing fees for aircraft. Methods and apparatus for reducing the exhaust gas levels of pollutants emitted from gas turbine engines, particularly oxides of nitrogen (NOx), carbon monoxide (CO), unburned hydrocarbons and smoke, are required to meet both current and anticipated emissions regulations for engine certification, as well as reducing engine cost of ownership issues in areas where emissions-based landing fees are imposed on customer's aircraft.
Most modern approaches for reducing gas turbine exhaust emissions are based on limiting the peak flame temperatures produced in the primary mixing zone of the combustor. Tight control of the primary zone flame temperature, however, requires that fuel and primary zone air be mixed as thoroughly and rapidly as possible prior to combustion in order to avoid local hot spots which produce high NOx levels.
The problem of rapidly and thoroughly mixing the fuel and primary zone air has been addressed by the addition of swirlers at the site of fuel injection. For example, axial swirlers have been mounted inside and outside of an injector body of a mixer for use in the combustion chamber of a gas turbine engine. Alternatively, swirl cups have been used to mix fuel and air in which swirlers are located adjacent to one another downstream from a single fuel injector. While the air-fuel mixers of the prior art have helped to decrease undesirable emissions, combustion performance can be further improved upon by increasing the efficiency of mixing fuel and primary zone air prior to combustion of the fuel.
Therefore, there is a need for an air-fuel mixer with an increased efficiency of mixing fuel and primary zone air. There is a further need for an efficient air-fuel mixer that can be used with various types of gas turbine engines.